GHSA-CRQ7-3PJ4-2VVG
Vulnerability from github – Published: 2026-09-16 12:30 – Updated: 2026-09-16 12:30In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping
While VNCR TLB invalidation always occurs under the MMU lock, vcpu_put() doesn't, while it unmaps the VNCR page.
The problem is that the invalidation evaluates vncr_tlb::cpu to decide whether an unmapping needs to take place (cpu != -1) before performing it. On the other hand, this_cpu_reset_vncr_fixmap() unconditionally unmaps if L1_VNCR_MAPPED is set.
These two obviously can race, with a TOCTOU pattern on the TLBI path, and a BUG_ON() on the vcpu_put() path. And the two can end-up calling vncr_fixmap(-1), with extra lethal effects.
Move the reset of vncr_tlb::cpu to -1 to a common function, and make this update atomic so that only a single thread can reset the field and perform the corresponding unmap. The vcpu_put() still need to unconditionally unmap the current VNCR to close another ugly race.
Finally, the assignment of vncr_tlb::cpu is moved to be kept in sync with the actual mapping, similar to L1_VNCR_MAPPED being set.
{
"affected": [],
"aliases": [
"CVE-2026-89917"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T11:17:00Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping\n\nWhile VNCR TLB invalidation always occurs under the MMU lock,\nvcpu_put() doesn\u0027t, while it unmaps the VNCR page.\n\nThe problem is that the invalidation evaluates vncr_tlb::cpu to\ndecide whether an unmapping needs to take place (cpu != -1) before\nperforming it. On the other hand, this_cpu_reset_vncr_fixmap()\nunconditionally unmaps if L1_VNCR_MAPPED is set.\n\nThese two obviously can race, with a TOCTOU pattern on the TLBI\npath, and a BUG_ON() on the vcpu_put() path. And the two can end-up\ncalling vncr_fixmap(-1), with extra lethal effects.\n\nMove the reset of vncr_tlb::cpu to -1 to a common function, and make\nthis update atomic so that only a single thread can reset the field\nand perform the corresponding unmap. The vcpu_put() still need to\nunconditionally unmap the current VNCR to close another ugly race.\n\nFinally, the assignment of vncr_tlb::cpu is moved to be kept in sync\nwith the actual mapping, similar to L1_VNCR_MAPPED being set.",
"id": "GHSA-crq7-3pj4-2vvg",
"modified": "2026-09-16T12:30:41Z",
"published": "2026-09-16T12:30:41Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89917"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/38640bc32be3fcf9526d477155bc19d3f146231f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5cbd8761d001c11ada73b1753d772c4745a70e72"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9065c1261f8a05c6a7a2d90048c7c0665ab2896d"
}
],
"schema_version": "1.4.0",
"severity": []
}
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